1. Field of the Invention
The present invention relates generally to a method and an apparatus for producing an active carbon using a carbon-containing material inclusive of an used active carbon. More particularly, the present invention relates to a method and an apparatus for producing an active carbon using a carbon-containing material inclusive of an used active carbon wherein the active carbon is produced by utilizing a power of electricity induced by electric discharge as well as a function of self-heating derived from electric resistance of an intermediate product of carbonized material with its own electric resistance.
2. Description of the Related Art
To produce an active carbon on the industrial basis, a plant based raw material such as wood chip, pulverized wood waste derived from sawing operations, liquid pulp waste, palm nut shells or the like and a mineral based raw material such as coal, petroleum coke, petroleum pitch or the like have been hitherto used. In addition, a waste material such as polyvinyl chloride resin and used tire can be used as a raw material for producing an active carbon after it is treated by employing a suitable method of allowing it to have electric conductivity. In practice, palm nut shells have been used as a most preferably employable raw material.
A so-called gas activating method has been hitherto known as one of methods each of treating palm nut shells to produce an active carbon. This method is practiced such that palm nut shells are indirectly heated up to an elevated temperature of 850 to 1000.degree. C. in an airless state by using a combustion gas generated by an oil burner and the surface of the heated palm nut shells is then eroded by reaction of the palm nut shells with steam thereby to form a porous structure having a number of fine pores.
In addition, a method of producing an active carbon using an used active carbon as a raw material by inducing arc discharge through a layer of used active carbon so as to regenerate the same to resume its original active state has been disclosed in an official gazette of Japanese Publication Patent NO. 21722/1981.
With respect to the former prior method, since the reaction for act the heated palm nut shells is composed of an endothermic reaction derived from a reaction of steam with carbon dioxide and carbon and an exothermic reaction derived from a reaction of oxygen with carbon, it is difficult to properly control a reaction temperature during each of the foregoing reactions. Additionally, since the palm nut shells are indirectly heated by using combustion gas generated by the oil burner, it is very difficult to properly control the reaction temperature, resulting in a quality of the resultant product of active carbon fluctuating. Consequently, an active carbon having a high quality can not be produced at a high yielding rate with this method. Another problem is that a long period of activating time, i.e., 6 to 20 hours is required at a working temperature of 850.degree. C., and therefore, an active carbon can not be produced not only at high efficiency but also at a low cost.
With respect to the latter prior invention, it is easy to properly control a step of activating compared with the former prior invention. As mentioned above, palm nut shells most preferably employable as a raw material have been hitherto carbonized within the range of 700 to 1000.degree. C. However, with the latter prior invention, there appears a problem that each carbonized palm nut shell has a part having electric conductivity and another part having no electric conductivity. In some case, the whole carbonized palm nut shell does not exhibit electric conductivity. In this case, carbonized palm nut shells can not be activated with power of electricity induced by electric discharge. Therefore, the latter prior method has been practically employed exclusively as a method of regenerating an used active carbon for the purpose of reusing the same.